The present specification relates generally to the field of displays. More specifically, the specification relates to integrity monitoring for head worn displays.
A head worn display (HWD) can be positioned in front of a user's eyes to provide operational capabilities similar to a fixed installation head up display (“HUD”). Head worn displays (e.g., helmet mounted displays, eyewear mounted displays, etc.) can provide information that is viewable in virtual space for the operation of equipment, such as aircraft, ships, boats, naval crafts, medical equipment, robotic equipment, remote vehicles, unmanned vehicle systems (“UVS”), training simulators, entertainment systems, military equipment, land vehicles, etc. The information can include navigation parameters, guidance parameters, equipment parameters, location information, video information, remote views, symbology, etc.
Head worn displays can be used to overlay display symbology (e.g., one or more symbols) onto scenes viewable out of a window or other port. The symbols are intended to represent or enhance features in the view of the user and are projected to a combiner. For the symbology to remain conformal with the view through the combiner on a head worn display, the head worn display generally tracks the head position. A head tracker sensor assembly is generally integrated with the head worn display and includes sensors that provide head position measurements for aligning the conformal symbology presented on the combiner with the view of the pilot based on the orientation of the user's head. Generally, head tracker sensor assembly can measure the following values: x (lateral) position, y (vertical) position, z (horizontal) position, roll (left/right tilt) angle, pitch (up/down tilt) angle and yaw (rotation) angle.
In aircraft applications, head worn displays generally include a computer (e.g., a HUD computer) that utilizes the values from the head tracker sensor assembly to determine the pilot's head position relative to an aircraft frame of reference (e.g., the bore sight) and the orientation of the aircraft relative to the ground provided by an attitude and heading reference system (“AHRS”) or inertial reference system (INS). Head position (e.g., x, y, z, roll, pitch, and yaw) measurement values are combined with associated parameters measured for the aircraft by the AHRS/IRS and transformed into earth (ground) frame. After this transformation to the ground frame, HWD symbology can be positioned on a combiner to overlay specific features of a real world scene as viewed through the combiner. For example, runway symbols can be displayed on the combiner that overlay the actual runway that the aircraft is approaching.
Assurance that information presented on a combiner correctly overlays the corresponding real world features is desirable prior to displaying that information to the user. For example, display functions can be monitored and redundant aircraft sensors can be utilized in fixed installation HUDs to ensure that symbols are properly positioned on the combiner. U.S. Pat. No. 4,698,785, incorporated herein by reference in its entirety, discloses a digital-based control data processing system for detecting during system operation the occurrence of data processing errors for HUDs. U.S. Pat. No. 7,212,175, incorporated herein by reference, also discloses a display presentation monitor for HUDs. An inverse algorithm can convert symbol position back to values of input parameters of aircraft orientation sensors which were used to position the symbol. The inverse values are compared to the actual input values associated with aircraft orientation sensors to determine if there is an unacceptable discrepancy. However, head tracking functions are currently not monitored for integrity in head worn display systems.
Thus, there is a need to determine head tracking errors in head worn displays. Further, there is a need to maintain a required level of integrity for aircraft applications in an head worn displays. Further still, there is a need for integrity monitoring of head worn displays that utilizes redundant head monitoring sensors. Further still, there is a need for a low cost integrity monitor and method for head worn displays. Yet further still, there is a need to determine symbology errors caused by head tracking sensors.